Known resonance-type light deflector devices that have hitherto been proposed have the following advantages that characterize them when compared with scanning optical devices employing a rotary polygon mirror. Namely, they can be remarkably downsized and consume less power and the variation in elevation angles of their mirror surfaces are theoretically free.
On the other hand, since the deflection angle (displacement angle) of the mirror of a resonance-type light deflector device changes in a sinusoidal manner in principle, its angular velocity is not constant. International Publication No. WO2005/063613 discloses a technique of forming a region where the angular velocity of the mirror is substantially constant by correcting this characteristic drawback.
More specifically, PCT International Publication WO2005/063613 discloses a micro-oscillating member comprising a plurality of torsion springs and a plurality of movable elements and having a plurality of isolated characteristic oscillation modes in a device. The plurality of isolated characteristic oscillation modes of the micro-oscillating member include a reference oscillation mode that is a characteristic oscillation mode of a reference frequency and even numbered oscillation modes that are characteristic oscillation modes of approximate even number times of the reference frequency. The invention of PCT International Publication WO2005/063613 realizes saw-tooth wave drive by oscillating the micro-oscillating member in those oscillation modes.
Japanese Patent Application Laid-Open No. 2005-292627 discloses a technique of detecting the clock time when a deflected scanning light beam passes a predetermined position by means of a light sensor in order to detect the scanning position of the light beam that is deflected by a deflector mirror driven to oscillate in a sinusoidal manner and controlling the state of oscillation of the deflector mirror, using the clock time.